Sforno on Genesis 8:7/ספורנו על בראשית ח׳:ז׳

1וישלח את העורב, to find out if the atmosphere had dried out after the tops of the mountains had become visible. Noach wanted to know if the atmosphere in the meanwhile was such that the raven could tolerate it.

2ויצא יצוא ושוב, this proved that the atmosphere was not yet dry enough for the raven to tolerate it for any extended period of time.